JP2008172099A - Core for antenna, and antenna - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To efficiently and inexpensively provide a core for an antenna ensuring high performance and easy form processing, which is used for a small and high sensitive coil antenna. <P>SOLUTION: This invention relates to the core for the antenna which is used for the coil antenna and is formed by using soft magnetism metal powder as a binding material and by using resin, wherein any insulated treatment is not applied to the soft magnetism metal powder itself and a filling factor of the soft magnetism metal powder is raised to the extent that the soft magnetism metal powders electrically conduct. As a result, an effectual permeability of the core for the antenna is improved beyond a loss caused by an eddy current and a high L value is realized with a small number of coil turns. As it is unnecessary to apply the insulated treatment to the soft magnetism metal powder, the core for the antenna ensuring high performance and easy form processing can be inexpensively provided. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an antenna core used for a small coil antenna. More specifically, the present invention relates to an antenna core and a coil antenna formed by winding a conductor around the antenna core, which is particularly preferably used for radio waves having a frequency in a range of 30 to 200 kHz called a long wave (LF) band.

Since the shape processing is easy, an antenna core in which a soft magnetic metal powder is molded using a resin as a binder is known.
Generally, in order to improve the characteristics of the antenna core, it is effective to increase the filling rate of the soft magnetic metal powder forming the core. However, when soft magnetic metal powders are in contact with each other and become electrically conductive, eddy currents are generated in the entire core and loss increases. Therefore, the surface of the soft magnetic metal powder may be oxidized or coated with resin. Insulating treatment is widely performed.

Japanese Patent Laying-Open No. 2001-337181 (Patent Document 1) discloses an invention relating to an antenna for a radio timepiece.
The first aspect of using the first composite material of Patent Document 1 as a rod-shaped core material is limited as being non-conductive in claim 1, and (0022) in the detailed description of the invention includes “ This first composite material may have conductivity when the ferrite or metal powder or flakes are 95 wt% or more, and the pair of connection pins provided on the obtained first flange are conductive. It is impossible to receive standard radio waves reliably. " This is because a pair of connecting pins for fixing both ends of a conducting wire wound as an antenna coil is directly provided on a rod-shaped core member used as an antenna core, so that it is necessary to ensure insulation at both ends of the conducting wire wound as an antenna coil. States that. Even if a pair of connection pins are provided directly on the rod-shaped core material used as the antenna core here, as long as non-conductivity sufficient to insulate both ends of the conducting wire wound as the antenna coil is ensured, Insulation between the soft magnetic metal powders forming the core is also ensured, so that eddy currents do not spread throughout the antenna core.
Regarding the aspect according to claim 8 in which the rod-shaped core material is formed in a hollow and the second composite material is inserted into the hollow portion, in the detailed description of the invention (0011), “the magnetic member is notable at the frequency of the radio timepiece. It only needs to be non-conductive so as not to generate eddy currents. "

Japanese Patent Laying-Open No. 2005-317664 (Patent Document 2) discloses an antenna core used for a coil antenna, which is composed of an insulating soft magnetic material having a soft magnetic powder and an organic binder. Is disclosed. In Patent Document 2, the purpose of making the soft magnetic material used for the antenna core insulative is described as “in order to suppress eddy current loss” in (0032) of the detailed description of the invention.
Japanese Patent Laying-Open No. 2005-333516 (Patent Document 3) uses a core made of an insulating soft magnetic material containing soft magnetic powder and an organic binder in a coil antenna wound around a core. A coil antenna is disclosed. The purpose of making the core used for the coil antenna in Patent Document 3 as an insulating soft magnetic material is described in (0023) in the detailed description of the invention, and in the case of conductive powder such as iron aluminum silicon alloy (Sendust). An oxide film is formed on the surface to prevent eddy currents. In the case of carbonyl iron or the like, eddy currents can be prevented by using an insulating coating with an organic binder. "

JP 2001-337181 A JP 2005-317664 A JP 2005-333516 A

In this way, for antenna cores that are molded using resin as a binder with soft magnetic metal powder, the filling rate of soft magnetic metal powder has been increased in order to improve its characteristics and eddy current loss has been suppressed. In order to achieve this, measures such as oxidizing the surface of the soft magnetic metal powder and applying an insulating coating with a resin have been taken.
However, there is a problem that such an insulation process increases the number of processes and costs. In addition, even when soft magnetic metal powder that has been subjected to insulation treatment is used, when using a molding method in which the filling rate of the soft magnetic metal powder is high and pressure is applied during molding of the antenna core, the soft magnetic metal powder In some cases, they are electrically connected to each other.
It is an object of the present invention to provide an antenna core with high performance and easy shape processing at low cost by efficiently producing a soft magnetic metal powder without subjecting it to insulation treatment.

As a result of intensive studies, the inventors of the present application have increased the filling rate of the soft magnetic metal powder used for the antenna core, thereby causing electrical conduction between the soft magnetic metal powders, and vortices throughout the antenna core. Even when a current is generated, surprisingly, in the case of a relatively low medium wave having a frequency of about 200 kHz or less, the effective permeability is improved by increasing the filling rate of the magnetic metal powder, and the eddy current It has been found that the loss due to the above can be compensated and the performance can be further improved, and the present invention has been completed.
In the antenna core of the present invention, the soft magnetic metal powder itself is not subjected to insulation treatment, and the filling rate of the soft magnetic metal powder is increased to such an extent that the soft magnetic metal powder is electrically connected to each other. Although it occurs in the entire core, the effective magnetic permeability of the antenna core is improved, so that a high L value can be realized with a small number of coil turns.

The effect of the present invention is to improve the effective magnetic permeability by increasing the filling rate of the soft magnetic metal powder, and to improve the receiving sensitivity of the antenna after subtracting the loss due to the eddy current. Therefore, it is possible to provide a highly sensitive antenna core as compared with the prior art. Moreover, since it is not necessary to insulate the soft magnetic metal powder, the antenna core can be provided at a low cost. Furthermore, since the soft magnetic metal powders are made conductive, there is an advantage that a molding means for performing molding while applying pressure can be employed.
An antenna formed by winding a conductive wire around the antenna core of the present invention is excellent in transmission sensitivity, reception sensitivity, and transmission / reception sensitivity, and is inexpensive.
By using the antenna of the present invention, it has become possible to provide a keyless entry system / immobilizer for automobiles, a tire pressure monitoring system, a radio timepiece, an RFID system, an electronic article monitoring system, etc. as a small and inexpensive one. .

Although the mechanism of the effect of the present invention is not necessarily clear, the reception sensitivity of the antenna is proportional to the product L × Q value of the L value and the Q value. In the present invention, it is considered that a high antenna sensitivity is manifested by improving the L value more than the loss caused by eddy currents by increasing the effective magnetic permeability of the core.
The Q value is represented by ω × L / R, where ω is 2 × π × f, where f is the frequency used, and R is the resistance of the conductor wound as a coil and the magnetic loss of the core. It is sum. The core magnetic loss is mainly the sum of hysteresis loss and eddy current loss. Although the loss due to the eddy current is increased in the present invention, the L value is improved more than the decrease in the Q value due to the eddy current. Therefore, it is considered that the performance is improved.
Since the antenna core of the present invention can obtain a high L value with the same number of turns, the antenna characteristics are improved. On the other hand, when the same L value is set, since the length of the winding can be remarkably shortened compared to the conventional antenna core that maintains the insulation property, the resistance of the conducting wire can be remarkably reduced. The value can be improved. Alternatively, when the same winding space can be used, since the number of windings is small, the wire diameter of the conducting wire can be increased and the winding resistance R is further reduced, so that the Q value can be further improved.

The filling ratio of the soft magnetic metal powder to the resin used as the binder is preferably 55 to 95% by weight. More preferably, the range of 60 to 95% by weight is used.
When the filling rate of the soft magnetic metal powder is low, there is a problem that the magnetic performance is low and the antenna characteristics are low. When the filling rate of the soft magnetic metal powder is low and the volume resistivity of the molded antenna core is larger than 10 Ω · m, good antenna characteristics cannot be obtained.
On the other hand, when the filling is high to 95% by weight or more, the amount of the binder is reduced, and the strength of the antenna core is lowered, so that the drop strength is lowered and the yield in the process is deteriorated. Problems occur. Regarding the lower limit of the volume resistivity of the antenna core of the present invention, the bulk volume resistivity of the soft magnetic metal powder to be used is the lower limit, but a binder that is a resin to ensure the necessary strength of the antenna core When about 5% is used, the volume resistivity is about 10 ⁻⁴ Ω · m or more.

If the soft magnetic metal powder is electrically connected by increasing the filling rate of the soft magnetic metal powder, an eddy current loss occurs and the loss increases. On the other hand, by increasing the filling factor, the effective magnetic permeability as a magnetic material is improved, and the number of windings of the conducting wire wound around the antenna core can be reduced. By reducing the loss due to the reduction in the number of turns, the antenna sensitivity can be effectively improved.
In the present invention, the core being conductive means a state in which the entire core is conductive and an eddy current is generated in the entire core.
The loss due to eddy current increases in proportion to the square of the frequency. Above 200 kHz, the loss due to eddy current increases remarkably, so the antenna characteristics deteriorate rapidly.
Therefore, good antenna characteristics can be obtained by setting the frequency band to be used to 200 kHz or less, preferably 150 kHz or less, and more preferably 100 kHz or less.

  As the soft magnetic metal powder used in the present invention, an amorphous alloy containing nanocrystals, an iron-based amorphous alloy, or a cobalt-based amorphous alloy can be suitably used. Also, using iron aluminum silicon alloy (Sendust), iron nickel alloy (permalloy), iron cobalt alloy, iron cobalt silicon alloy, iron silicon vanadium alloy, iron cobalt boron alloy, carbonyl iron, molybdenum permalloy, pure iron dust, etc. It doesn't matter. These may be used alone or as a mixture of a plurality of soft magnetic metal powders.

And more specifically for amorphous alloys or iron-based amorphous alloy containing suitably nanocrystals used, the general formula _{(Fe 1-x M x)} 100-a-b-c-d Si a Al b B c M 'd Where M is Co and / or Ni, M ′ is Nb, Mo, Zr, W, Ta, Hf, Ti, V, Cr, Mn, Y, Pd, Ru, Ga, Ge, One or more elements selected from C, P, Cu, Au, Ag, Sn, and Sb, x represents an atomic ratio, a, b, c, and d represent atomic%, and 0 ≦ x ≦ 0. 5, soft magnetic metal powder containing nanocrystals having a crystallite diameter of 100 nm or less obtained by heat-treating amorphous alloy powder satisfying 0 ≦ a ≦ 24, 0 ≦ b ≦ 20, 1 ≦ c ≦ 30, and 0 ≦ d ≦ 10 It is preferable that
Alternatively, it is represented by the general formula (Fe _1-x Co _x Ni _y ) _100-a-b-c Si _a B _b M _c , where M is Nb, Mo, Zr, W, Ta, Hf, One or more elements selected from Ti, V, Cr, Mn, Y, Pd, Ru, Ga, Ge, C, P, Al, Cu, Au, Ag, Sn, and Sb, and x and y are atomic ratios. A, b and c represent atomic%, and 0 ≦ x ≦ 1.0, 0 ≦ y ≦ 0.5, 0 ≦ x + y ≦ 1.0, 0 ≦ a ≦ 24, 1 ≦ b ≦ 30, An amorphous alloy powder satisfying 0 ≦ c ≦ 30 or an amorphous alloy powder containing nanocrystals can be exemplified.

An amorphous alloy can be obtained by melting a metal material blended to have a desired composition at a high temperature using a high-frequency melting furnace or the like to form a uniform molten metal and quenching it. A ribbon-shaped amorphous alloy is obtained by spraying molten metal on a rotating cooling roll. Amorphous alloy powder can be obtained by pulverizing this, but it is preferable to use a pulverization method in which stress is not applied because the magnetic properties often deteriorate due to stress during pulverization.
Specifically, an amorphous alloy powder free from stress can be obtained by using a water atomizing method in which melting is directly poured into water or a gas atomizing method in which a large amount of gas is blown and cooled. Further, when the gas atomization method is used, a flat amorphous alloy powder, which will be described later, can be obtained by causing particles atomized with gas to collide with a conical rotating cooling body.

    The amorphous alloy powder containing nanocrystals can be prepared by applying an appropriate heat treatment to the above-described amorphous alloy powder. The heat treatment conditions depend on the composition of the alloy and the magnetic properties to be expressed, but the amorphous alloy powder is treated at a temperature higher than the crystallization temperature at a temperature of approximately 300 to 700 ° C. for several tens of seconds to several hours. It is possible to deposit nanocrystals. This heat treatment is preferably performed in an inert gas atmosphere. The production state of nanocrystals can be evaluated by measuring powder X-ray diffraction. An amorphous alloy powder containing nanocrystals having a crystallite diameter of 100 nm or less calculated from the half width of the diffraction peak of powder X-ray diffraction by the Scherrer equation can be preferably used.

The soft magnetic metal powder used in the present invention may be spherical, acicular or irregular, but preferably has a flat shape such as a disk or an ellipse. If it is flat, it may be indefinite. In particular, it is preferable to have a flat shape with a thickness of 10 μm or less, more preferably a flat powder with a thickness of 5 μm or less and a particle size of 300 μm or less, more preferably a thickness of 5 μm or less and a particle size of 200 μm or less. A flat powder is preferred.
The soft magnetic metal powder used in the present invention may be a powder having substantially the same shape, but may be used by mixing powders having different shapes within the range where the effects of the present invention are exhibited. There is no.
The soft magnetic metal powder used in the present invention may be a soft magnetic metal powder that has been surface-treated with a coupling agent or the like in advance.

The resin used as the binder in the present invention may be any resin that can bind the magnetic metal powder when filled at a high filling rate, and a wide range of thermosetting resins and thermoplastic resins can be used. These resins are usually insulating by the resin alone.
If a thermosetting resin is illustrated, an epoxy resin, a phenol resin, an unsaturated polyester resin, a urethane resin, a urea resin, a melamine resin, a silicone resin, etc. can be used conveniently.
Examples of thermoplastic resins include polyethersulfone, polyetherimide, polyimide, polyetherketone, polyethylene terephthalate, nylon, polybutylene terephthalate, polycarbonate, polyphenylene ether, polyphenylene sulfide, polysulfone, polyamide, polyamideimide, polylactic acid, Polyethylene, polypropylene and the like can be suitably used.
Any thermoplastic resin can be used as it is, or a plurality of thermoplastic resins may be mixed and used. Moreover, if it is a thermosetting resin, normally, 2 types of resin of a main ingredient and a hardening | curing agent are mix | blended and used. A thermosetting resin or a mixture of a plurality of resins may be used. Moreover, you may mix | blend and use flame retardants, such as a halide, as needed.
Among these resins, epoxy resin or phenol resin is particularly preferably used for thermosetting resins and polyether sulfone is particularly preferably used for thermoplastic resins because of excellent dimensional stability after molding.
Among thermosetting resins, those having a high curing rate and capable of being used for injection molding, transfer molding and the like are preferable.

The mixing of the thermosetting resin powder used as the binder and the soft magnetic metal powder can be performed as follows. That is, the powders of the main agent and the curing agent to be the thermosetting resin are mixed. For this mixing, various conventionally known mixers, mixers, and the like can be used. When mixing a main ingredient and a hardening | curing agent, you may mix | blend a hardening accelerator, a mold release agent, etc. as needed.
Next, the thermosetting resin powder in which the main agent and the curing agent are mixed and the soft magnetic metal powder are mixed. Compared to mixing the main component and curing agent of thermosetting resin, mixing of thermosetting resin powder mixed with main component and curing agent and soft magnetic metal powder has a large difference in specific gravity. Therefore, it is necessary to set mixing conditions such as mixing time.
When a thermoplastic resin is used, when a single thermoplastic resin is used, the thermoplastic resin powder and the soft magnetic metal powder may be mixed so as to be sufficiently uniform. When a plurality of thermoplastic resins are mixed and used, a plurality of thermoplastic resins are mixed in advance and then mixed with the soft magnetic metal powder so as to be sufficiently uniform. Moreover, you may mix | blend additives, such as a mold release agent.
The soft magnetic metal powder used in the present invention may be one that has been surface-treated with a coupling agent or the like in advance.

Compression molding machine and injection molding machine using precursors molded into tablets, columns, granules, or pellets using mixed powders of resin powder and soft magnetic metal powder mixed to be sufficiently uniform Alternatively, the antenna core is molded using a transfer molding machine or the like. Alternatively, the antenna core may be molded using the molding machine or the like by directly using a mixed powder of resin powder and soft magnetic metal powder mixed so as to be sufficiently uniform.
There are optimum molding conditions depending on the resin used and the filling rate of the soft magnetic metal powder, etc., but when a normal thermosetting resin is used, it is generally in the temperature range of 50 to 300 ° C., preferably 100 to 200 ° C. Molded in the temperature range. The pressure during molding can be molded within a pressure range of 0.1 to 300 MPa, and preferably molded within a pressure range of 1 to 100 MPa. The curing time can be in the range of about 5 seconds to 2 hours, and other molding conditions are preferably adjusted so that the molding is preferably performed in a time range of 30 seconds to 10 minutes.
In order to complete the curing of the thermosetting resin, it is preferable to perform an annealing treatment after the molding. The annealing conditions vary depending on the thermosetting resin to be used, but are usually applied in a temperature range of 100 to 250 ° C. with a pressure released in a time range of about 1 minute to 10 hours.
Annealing may be performed in the mold, or may be performed by removing from the mold. By removing from the mold and annealing, continuous molding becomes possible, and productivity can be improved.

As the thermosetting resin, a liquid thermosetting resin may be used. When a liquid thermosetting resin is used, a liquid thermosetting resin main ingredient and a curing agent are blended, and usually a curing accelerator is further added, and a mold release agent is added if necessary. A flame retardant may be added.
A mixed liquid thermosetting resin and soft magnetic metal powder previously mixed are put in a mold and molded by a molding machine. When the solvent is contained, the molding is performed after the solvent is volatilized. Alternatively, after removing the solvent by volatilization in advance, it may be placed in a mold and molded by a molding machine.
An antenna is formed by winding a conductive wire around these antenna cores. At this time, an insulation process is performed on the portion to be wound as necessary. As the insulation treatment, an insulating resin may be coated, or an insulating tape, film, or the like may be wound.

Hereinafter, the details of the present invention will be described more specifically with reference to examples. However, the present invention is not limited to these examples.
(Example 1)
An alloy having the composition of Fe ₆₆ Ni ₄ Si ₁₄ Al ₄ B ₉ Nb ₃ is melted at 1300 ° C. using a high-frequency melting furnace, and the molten metal is allowed to flow through a nozzle attached to the bottom of the melting furnace, and provided at the tip of the nozzle. The molten metal was atomized from the gas atomizing portion using 75 kg / cm ² of high-pressure argon gas, and the atomized molten metal was allowed to collide with a conical rotating cooling body having a roll diameter of 190 mm, apex angle of 80 degrees, and rotation speed of 7200 rpm. Then, a flat soft magnetic metal powder having an average major axis of 150 μm, an average minor axis of 55 μm, and an average thickness of 2 μm having a composition of Fe ₆₆ Ni ₄ Si ₁₄ Al ₄ B ₉ Nb ₃ was produced. This soft magnetic metal powder was heat-treated at 550 ° C. for 1 hour in a nitrogen gas atmosphere. As a result of measuring the X-ray diffraction of the soft magnetic metal powder after the heat treatment, a slightly broad diffraction peak appears, and the crystallite size calculated from the half-value width of the diffraction peak using the Scherrer equation is approximately 20 nm. there were.
The binder used in Example 1 of the present invention is Nippon Kayaku Co., Ltd. epoxy resin: trade name EOCN-102S, and 100 parts by weight of this hardener: Mitsui Chemicals, Inc .: trade name 61 parts by weight of Millex XCL-4L was added, and 5 parts by weight of trade name 3502T with respect to the epoxy resin and a small amount of release agent were added as a curing accelerator, and the mixture was pulverized and mixed with a mixer.
The previously prepared soft magnetic metal powder was used as it was without being subjected to insulation treatment, and was treated with a silane coupling agent in order to improve the adhesion to the resin. 5 parts by weight of silane coupling agent manufactured by Shin-Etsu Chemical Co., Ltd. with respect to 100 parts by weight of epoxy resin: product KBM-403 is weighed, and enough to make the soft magnetic metal powder and the silane coupling agent uniform. Mixed. Using a soft magnetic metal powder mixed with a silane coupling agent, weighed the magnetic powder to a ratio of 90% by weight and mixed for 10 minutes to obtain a uniform mixed powder composed of the soft magnetic metal powder and the epoxy resin. It was.
All the mixers used for the mixing operation so far are hybrid mixers manufactured by Keyence Corporation. This mixer was also used in the following examples and comparative examples.
The prepared mixed powder of soft magnetic metal powder and epoxy resin is filled into an 80 mm × 10 mm mold so that the thickness after molding becomes 3.5 mm, heated and pressurized at a temperature and pressure of 150 ° C. and 50 MPa, 5 After a minute, the mold was opened, the antenna core material was taken out, and then annealed in an oven at 180 ° C. for 2 hours. A rectangular parallelepiped having a length of 18 mm, a width of 2.8 mm, and a thickness of 3.5 mm was cut out from the antenna core material. And the symmetrical recessed part by which the conducting wire used as a coil was wound in the center part was provided. The shape of the recess is 10 mm long, 1.8 mm wide, and 1.0 mm thick. Further, a 2.5 mm portion was trimmed in the length direction and the width direction from one end of each end portion that became the protruding portion, and processed into the shape shown in FIG.
Further, in order to measure the volume resistivity of the antenna core, a rectangular parallelepiped having a length of 10 mm, a width of 3 mm, and a thickness of 3 mm was cut out from the same antenna core material. The volume resistivity of the rectangular parallelepiped was 1.9 × 10 ⁻³ Ω · m when measured using a TR6847 multimeter manufactured by Advantest Corporation. Note that the volume resistivity measurement is not a uniform metal material, but the resistivity shows a value close to that of metal. The resistivity was calculated. From the volume resistivity value, it was confirmed that there was continuity throughout the antenna core, and eddy currents were generated throughout the antenna core.
A Kapton tape was wound around a concave portion provided in the center of the antenna core, and 2000 turns were wound using a φ0.05 mm coated copper wire, and a Q value and an L value were measured at a frequency of 60 kHz. For measurement of the Q value and the L value, an LCR meter 4284A manufactured by Hewlett Packard Company was used, and the measurement voltage was set to 0.1V.
The results are shown in Table 1.

(Example 2)
In the same manner as in Example 1 except that the alloy composition of the soft magnetic metal powder was Fe ₄ Co ₆₆ Ni ₁ Si ₁₅ B ₁₄ , the molten metal atomized was collided with the rotating cooling body and rapidly cooled to obtain an average major axis of 70 μm. A flat soft magnetic metal powder having an average minor axis of 20 μm and an average thickness of 3 μm was prepared.
The produced soft magnetic metal powder was held at a temperature of 400 ° C. for 1 hour under a nitrogen stream to perform heat treatment for improving the soft magnetic properties. When the powder X-ray diffraction was measured, it was confirmed to be an amorphous phase in which the nanocrystalline phase was not mixed.
Polyether sulfone pellets manufactured by Mitsui Chemicals Co., Ltd. were freeze-pulverized to produce polyether sulfone resin powder having an average particle size of 100 μm. The soft magnetic metal powder and the resin powder were mixed for 10 minutes so that the soft magnetic metal powder was 84% by weight to prepare a mixed powder of the soft magnetic metal powder and the resin powder. The mixed powder was filled in the mold used in Example 1, heated to 350 ° C., maintained at 350 ° C., a pressure of 15 MPa was applied for 10 minutes, and the core material was cooled to 150 ° C. while the pressure was applied. I took it out. Using the obtained core material, an antenna core was produced in the same manner as in Example 1, and wound to evaluate the characteristics. The results are shown in Table 1. The volume resistivity of the core material was 2.5 × 10 ⁻³ Ω · m, and it was confirmed that the core material had conductivity.

(Example 3)
An antenna core was produced in the same manner as in Example 1 except that Hitachi Metals, Ltd., trade name: Finemet magnetic powder FP-FT-5M was used as the soft magnetic metal powder. The composition of finemet magnetic powder has not been clarified, but according to the catalog of Hitachi Metals, high-temperature melting of a unique composition consisting mainly of iron, with addition of Si and B, and trace amounts of Cu and Nb. An amorphous ribbon obtained by rapidly cooling and solidifying a liquid at about 1 million ° C./second is a magnetic powder containing an amorphous phase in which nanocrystals of about 10 nm are deposited by heat treatment at a temperature higher than the crystallization temperature.
The volume resistivity of the core material was 2.2 × 10 ⁻³ Ω · m, and it was confirmed that the core material had conductivity.
The L value and Q value of the antenna were measured in the same manner as in Example 1. The results are shown in Table 1.

Example 4
An antenna core was manufactured in the same manner as in Example 3 except that the soft magnetic metal powder was used in a proportion of 83% by weight. The volume resistivity of the core material was 6.3 × 10 ⁻³ Ω · m, and it was confirmed that the core material had conductivity. The L value and Q value of the antenna were measured in the same manner as in Example 1. The results are shown in Table 1.

(Example 5)
An antenna core was produced in the same manner as in Example 3 except that the soft magnetic metal powder was used in a proportion of 70% by weight. The volume resistivity of the core material was 5.4 × 10 ⁻² Ω · m, and it was confirmed that the core material had conductivity. The L value and Q value of the antenna were measured in the same manner as in Example 1. The results are shown in Table 1.

(Comparative Example 1)
An antenna core was produced in the same manner as in Example 3 except that the soft magnetic metal powder was used in a proportion of 50% by weight. The volume resistivity of the core material was 3 × 10 ⁵ Ωm (measurement limit) or more, and it was confirmed to be insulating.
Although this core material has a range in which insulation can be secured, since the filling amount of the soft magnetic metal powder cannot be increased, both the L value and the Q value are lower than those of the examples, and the antenna characteristics are deteriorated.

(Comparative Example 2)
An antenna core was produced in the same manner as in Example 3. The volume resistivity of the core material was 2.2 × 10 ⁻³ Ω · m of Example 3, and it was confirmed that the core material had conductivity.
Similar to the first aspect of the invention disclosed in Patent Document 1, two holes of φ0.8 mm were formed in the end portion of the antenna core, and a pair of metal pins were press-fitted into terminals. In the same manner as in Example 1, the coated copper wire was wound around the antenna core for 2000 turns, and then the ends of the coated copper wire were connected to the metal pins by soldering.
In this antenna, the resistance of the coated copper wire wound is about 180Ω, whereas the resistivity of the core material is as low as 2.2 × 10 ⁻³ Ω · m. It did not function as an antenna.

In the present invention, the effective magnetic permeability is improved by increasing the filling rate of the soft magnetic metal powder, and the reception sensitivity of the antenna is improved despite the loss caused by the eddy current. Therefore, it is possible to provide a highly sensitive antenna core as compared with the prior art. Moreover, since it is not necessary to insulate the soft magnetic metal powder, the antenna core can be provided at a low cost. Furthermore, since the soft magnetic metal powders are made conductive, there is an advantage that a molding means that performs molding while applying pressure can be employed.
An antenna formed by winding a conductive wire around the antenna core of the present invention is excellent in transmission sensitivity, reception sensitivity, and transmission / reception sensitivity, and is inexpensive.
By using the antenna of the present invention, it has become possible to provide a keyless entry system / immobilizer for automobiles, a tire pressure monitoring system, a radio timepiece, an RFID system, an electronic article monitoring system, etc. as a small and inexpensive one. .

It is a top view which shows the shape of the core for antennas used in the Example.

Claims (14)

  An antenna core for use in a coil antenna, which is obtained by molding a soft magnetic metal powder using a resin as a binder, wherein the core is conductive. The antenna core according to claim 1, wherein the core has a volume resistivity of 1 × 10 ⁻⁴ Ω · m to 10 Ω · m.   3. The antenna core according to claim 1, wherein the soft magnetic metal powder is at least one soft magnetic metal selected from the group consisting of an amorphous alloy containing nanocrystals, a cobalt-based amorphous alloy, and an iron-based amorphous alloy. An antenna core, characterized by being a powder. An antenna core as claimed in claim 3, the soft magnetic metal powder, the general formula _{(Fe 1-x M x)} is represented by _100-a-b-c- d Si a Al b B c M 'd Where M is Co and / or Ni, M ′ is Nb, Mo, Zr, W, Ta, Hf, Ti, V, Cr, Mn, Y, Pd, Ru, Ga, Ge, C, P , Cu, Au, Ag, Sn, and Sb, x is an atomic ratio, a, b, c, and d are atomic%, and 0 ≦ x ≦ 0.5, 0 ≦ a ≦ 24, 0 ≦ b ≦ 20, 1 ≦ c ≦ 30, 0 ≦ d ≦ 10 is a soft magnetic metal powder containing nanocrystals having a crystallite diameter of 100 nm or less after heat treatment of amorphous alloy powder A core for an antenna. An antenna core as claimed in claim 3, the soft magnetic metal powder represented by the general formula _{(Fe 1-x Co x Ni} y) 100-a-b-c Si a B b M c, where In the formula, M is Nb, Mo, Zr, W, Ta, Hf, Ti, V, Cr, Mn, Y, Pd, Ru, Ga, Ge, C, P, Al, Cu, Au, Ag, Sn, Sb. X, y are atomic ratios, a, b, c are atomic%, and 0 ≦ x ≦ 1.0, 0 ≦ y ≦ 0.5, 0 ≦ x + y, respectively. An antenna core characterized by being an amorphous alloy powder satisfying ≦ 1.0, 0 ≦ a ≦ 24, 1 ≦ b ≦ 30, 0 ≦ c ≦ 30, or an amorphous alloy powder containing nanocrystals. 6. The antenna core according to claim 1, wherein the soft magnetic metal powder is a soft magnetic metal powder having a flat shape with a thickness of 10 μm or less.   The antenna core according to any one of claims 1 to 6, wherein the resin used as the binder is an epoxy resin and / or a polyether sulfone resin.   An antenna comprising a conductor core wound around the antenna core according to any one of claims 1 to 7.   The antenna according to claim 8, wherein the antenna is an antenna for transmitting, receiving, or transmitting / receiving a long wave of 30 to 200 kHz.   A keyless entry system for an automobile, wherein the antenna according to claim 9 is used as a transmission antenna, a reception antenna, or a transmission / reception antenna.     A tire pressure monitoring system using the antenna according to claim 9 as a transmission antenna, a reception antenna, or a transmission / reception antenna.   A radio timepiece using the antenna according to claim 9 as a receiving antenna.   A radio frequency identification system using the antenna according to claim 9 as a transmission antenna, a reception antenna, or a transmission / reception antenna.   10. An electronic article monitoring system, wherein the antenna according to claim 9 is used as a transmission antenna, a reception antenna, or a transmission / reception antenna.